A dental ceramic can be colored e.g. by incorporating pigments into the ceramic material from the very beginning or using metal salts containing solutions which are applied on the surface of a porous dental ceramic article with the aim to color the dental ceramic article in its entirety. Coloring solutions are described in a couple of documents:
WO 2004/110959 relates to a colouring solution for ceramic framework. The solution comprises a solvent (e.g. water), a metal salt and polyethylene glycol having a Mn in the range of 1.000 to 200.000.
WO 00/46168 A1 (corresponding to U.S. Pat. No. 6,709,694 B1) refers to colouring ceramics by way of ionic or complex-containing solutions containing defined concentrations of at least one salts or complexes of the rare earth elements or of the elements of the subgroups. The solution might contain additives like stabilizers, complex builders, pigments and beating additives.
WO 2008/098157 relates to a colouring solution for dental ceramic framework comprising a solvent, a colouring agent comprising metal ions, and a complexing agent, wherein the amount of complexing agent is sufficient to dissolve the colouring agent in the solvent.
WO 2009/014903 relates to a colouring solution for dental ceramic articles, the solution comprising a solvent and a colouring agent comprising rare earth element ions being present in the solution in an amount of at least about 0.05 mol/l solvent and transition ions being present in the solution in an amount of about 0.00001 to about 0.05 mol/l solvent.
J. Eschenbaum et al. describes in Solid State Ionics 77 (1995) 222-225 thin films or proton conducting SrZrO3-ceramics prepared by the sol-gel method.
Sometimes, however, it is also desirable to use a whitening agent. Whitening agents are typically used to cover the metallic surface of a metallic dental framework in order to give the final dental restoration a more natural appearance. In certain cases, it can also be desirable to opacify e.g. the inner surface of a ceramic framework to cover discolourations of the tooth stump.
Compositions for whitening or opacifying dental metallic restorations are available in the market. Those compositions typically form a separate layer on the surface of the metallic framework and do not become part of the framework. These compositions often contain titania as a whitening pigment to achieve the desired whitening effect.
The present invention is intended to improve the known colouring and/or whitening processes.